It should have lasted longer. But they had people opposed to this match, they kind of caused their own trouble by creating the love triangle and they danced around the triangle giving each some hope but it was always clear that Jack and Kate were going to end up together. The writer seemed to not want to lose fans that didn't want that. Even my mom when she watched said it was obvious that Kate and Jack loved each other
Sad they could not let us have more of them together, happy and in love